Most buyers meet knob and tube wiring as a line in an inspection report and file it under "things to fix eventually."
That is the wrong category, and the mistake costs people deals.
Some insurance carriers will not write a policy on a property with active knob and tube wiring. No policy means no closing, because your lender requires insurance as a condition of funding. So a wiring finding at day 12 becomes a financing emergency at day 22, with your deposit exposed.
What it is
Knob and tube is an early electrical wiring method — individual conductors run through ceramic tubes where they pass through framing, supported by ceramic knobs, with cloth-and-rubber insulation.
It was standard into roughly the 1940s. In Greater Boston's housing stock, where most buildings predate 1978 and a great many predate 1940, it is common — particularly in triple-deckers, brownstones, and unrenovated upper floors and attics.
Three characteristics matter:
No ground. Two-wire system, no equipment grounding conductor. That is why you see two-prong outlets.
Insulation degrades. The cloth and rubber becomes brittle with age and heat and can fail, especially at connection points and inside junction boxes.
It was designed for a 1930s electrical load. Not for the number of devices a modern household runs.
The specific hazard underwriters focus on: knob and tube was designed to dissipate heat into open air. Burying it in modern blown-in or batt insulation traps that heat, which is one reason an otherwise-stable system becomes a problem after a well-intentioned energy retrofit.
Why carriers care, and what they actually do
From an underwriting standpoint this is a fire-loss question, and carrier responses vary widely:
Decline outright. Some will not write it at all.
Require full replacement within a set period after binding.
Require an electrician's certification that the system is in safe working order, sometimes with photos.
Write it at a significantly higher premium, or with coverage limitations.
Write it without comment, which happens too, and is why buyers assume there is no issue until the carrier they actually want says no.
The practical problem is that you do not know which response you will get until you ask, and most buyers ask too late.
The timeline that goes wrong
Here is the sequence I see.
Day 1: offer accepted. In Massachusetts, a signed and accepted Offer to Purchase has been treated by courts as a binding contract, so you are committed early.
Day 8: inspection identifies active knob and tube in the attic and on the third floor.
Day 12: buyer and agent treat it as a repair negotiation and ask for a credit.
Day 20: buyer applies for homeowners insurance for the first time, because that is when people do.
Day 22: carrier declines, or conditions the policy on full replacement.
Day 24: purchase and sale signed, larger deposit now at risk, financing contingency date approaching, lender requires a binder, and nobody has a policy.
The fix is almost absurdly simple and almost nobody does it.
What to do instead
Get an insurance quote the same week as the inspection. Not the week of closing. Call your agent, tell them the truth — active knob and tube, partial, in the attic and third floor, here is the inspector's language — and ask what the carrier will do.
Get three quotes. Carrier appetite varies enormously, and a decline from one does not mean the property is uninsurable.
Get an electrician's scope and number, not an estimate range from the inspector. A licensed electrician walking the property will tell you what is actually active versus abandoned in place, which is frequently the whole question.
Ask what is abandoned. In a lot of Boston properties, previous owners rewired the main living areas and left dead knob and tube in the walls. Abandoned wiring that is disconnected is a materially different conversation than active circuits, and inspection reports are not always precise about which is which.
Check whether insulation was added over it. This is the specific condition underwriters dislike most, and it is common in buildings that received an energy retrofit.
What it costs to fix
Rewiring is priced by circuit count, access, and finish restoration — the wire is cheap, opening and patching walls and ceilings is not.
Partial work targeting active circuits in specific areas is a modest project. A full rewire of a triple-decker unit, or a whole building, is a significant one, and in a plaster building the restoration can exceed the electrical work.
Get a real scope from a licensed electrician before you negotiate, because the gap between a targeted fix and a full rewire is large, and sellers negotiate against numbers rather than concerns.
For sellers
If you own pre-war stock and you are listing, find out what your wiring is before a buyer's inspector tells you in writing during the highest-leverage week of your transaction.
Two options, and both are better than being surprised:
Have it assessed and disclose it accurately, with an electrician's scope attached. A disclosed, scoped, priced issue is a negotiation. A discovered one is evidence there may be more, and buyers price uncertainty worse than they price problems.
Or address the active circuits before listing, which removes the insurance objection entirely and widens your buyer pool to include every buyer whose carrier would have declined.
This is the clearest argument for a pre-listing inspection in Boston's housing stock. It converts a negotiation into a disclosure and moves the conversation to before the offer instead of after it.
For condo buyers
Two layers. Your unit's wiring, and the building's electrical service.
Ask about both. A building with an undersized main service is a capital project waiting to happen, and in a three-unit triple-decker conversion a service upgrade is divided three ways with no economy of scale.
Pull the reserve balance, read twelve to twenty-four months of minutes, and look specifically for electrical discussion. That is where a service upgrade appears a year before it becomes an assessment.
The one-line version
Knob and tube does not kill deals. Discovering the insurance consequence at day 22 kills deals.
Make the insurance call the same week as the inspection, and this becomes a number you negotiate rather than an emergency you survive.
If you are under agreement and knob and tube turned up, send me the inspection language and I will tell you what I would do about it and in what order. If you are shopping pre-war stock, I will tell you which questions belong in your offer.
Chris Remmes, Managing Broker, Remmes & Co. [email protected] | 617-398-0015
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